Why is marketing important?

The Mona Lisa was not valued as a masterpiece painting for most of its existence.
In fact, it was not even chosen as a top 100 painting in the museum nor was it considered one of Da Vinci's best works.

It was only when it was stolen that the fanfare caused it to become one of the most recognized and valuable paintings in the world. When it was finally recovered, it was welcomed with its own room and a hundred thousand viewers.
According to this video:

A study was done that found that what people see other people listening to and liking most has an effect on their opinion on which songs they like. One group was shown what other people liked, rated, and a top charts lists before rating songs. The control group did not have these extra options. Sure enough, it definitively affected their ratings. However, the song had to be good first. Quality mattered. But as long as you were in the top third of quality, anything could happen. An executive at Time Warner and head of Turner Broadcasting admits that he has no idea what will be a hit, though his team tries his best by using algorithms and trends. ___ Stephen King wrote some books under a psuedonym. When it was revealed it was him, sales went up ten times. Same book. A similar thing happened with J.K. Rowling. Their books bombed in sales. Marketing makes the magic happen. It gets the word out. Guess what? I recently bought a pizza because of a deal someone handed me on a flier. I would’ve never known about this if it wasn’t for that flier even though I wanted to buy the pizza if I knew about the offer. That’s marketing. There’s more to it of course (strategy, sales, positiong, etc.) but that’s the gist.